Chemistry 32A
FLAME TEST
Cover Sheet for
NOT in Sara Selfe Lab Manual, use handout provided
Student Name (please pirint)
Lab Section, Day and Time
Date report submitted
Please provide your Assessment of this experiment, including at least the following
What did you learn from the experiment?
Were the instructions clear and easy to follow?
Was there sufficient time to complete the experiment?
What were highlights and lowlights in performing this experiment?
-
CHEM 32A - Flame Test Identification of Elements* and Interpreting their
Spectral Lines Using a Spectroscope
Introduction:
The conventional, but simplified, atomic structure model describes the atom as a nucleus (protons
and neutrons) surrounded by electrons. You recently learned that the electrons are organized to exist
at specific allowed locations and distances from the nucleus with a corresponding specific energy
level, n. Most of the atoms of an element at room temperature are in their “ground state” which
means that electrons are arranged in a configuration representing the lowest possible total energy.
Modern medicine utilizes a number of non-invasive techniques other than “blood chemistry” to treat
patients. Various instruments use properties of radiation (e.g. infrared, MRI, CT-scans, x-ray, etc.) to
diagnose and monitor diseases such as certain cancers, Parkinson’s, Alzheimer’s, etc. We also
manipulate radiation in our everyday lives (think sunscreen, dark glasses, microwave ovens, cell
phones, TV brightness). You already own two sensitive radiation detectors, namely your eyes!
In this experiment you will visually observe the flame colors of 8 common elements using the flame
test and the emission line spectrum of elements in a gas discharge tube using a spectroscope. The
electrons of the element atoms initially in their ground state (lowest energy configuration) will be
excited to a higher energy level in the atom after absorbing energy first, from heat of a Bunsen
burner flame and second from electricity of a gas discharge tube. When the electrons in the atom
“relax” or fall back to their ground state location, they must give up the excess energy they
possessed in the excited state. This excess energy is given off in the form of the visible light you will
observe. The wavelength (color) of the light observed is a direct measure of the difference in energy
an electron possessed in the excited state relative to the ground state. Please refer to the “Atomic
Emission Animation” on YouTube at, http://www.youtube.com/watch?v=8TJ2GlWSPxI .
You will also observe that different elements have different line spectra (collection of emission
lines) or flame colors due to the different number and arrangement of the electrons in atoms of
different elements. The fact that different elements have individual characteristic flame colors and
emission line spectra can often be used to identify or verify the presence of a particular element. A
pathologist, for example, might use flame tests to screen for possible hazardous materials.
Part I. In the first part of this experiment, we will use a flame (heat) to excite the electrons in 8
“Known” samples so they will emit characteristic colors. These colors directly correlate to a
characteristic wavelength, λ frequency, υ and Energy, E. You will identify each color (remember
ROYGBIV) within the visible spectrum of the electromagnetic radiation and approximate the
wavelength using a reference chart (see last page of this handout for the visible spectrum within the
electromagnetic spectrum). Each one of the known elements will be recorded in your experiment
along with its characteristic emission color and wavelength.
Next, using the data from your flame tests (eg. color and estimated wavelength) and chart of line
emission spectra, identify 3 “Unknown” elements from comparing results from your group of 8
knowns. You will then convert the wavelengths of your three unknown samples to energy values
using the formula
E = ħυ
c = υλ and since, υ=c/ λ
E= ħc/λ
E = energy of light (photon)
ħ = Planck’s constant = 6.6261*10-34J·s
λ = wavelength in meters
c = speed of light 2.9979*108 m/s
A calculation example is provided on the data worksheet. Finally, you will plot the graphs of:
(a) wavelength observed versus the calculated energy and conclude an important relationship
between energy and wavelength, and be able to answer the question why we use sunscreen.
(b) frequency observed versus the calculated energy an conclude important relationship between
frequency and energy and contrast this with your graph in part (a) above.
Notes: For a flame test animation see, http://www.800mainstreet.com/spect/emission-flameexp.html#Anchor-barium. Free online graph paper can be downloaded at:
http://incompetech.com/graphpaper/plain/.
*Part I of this lab experiment was adopted from
http://www.csus.edu/indiv/m/mackj/chem1A/lab/pdfs/Exp_10.pdf . See also URLs at the end of this
module.
Part II. In this part of the experiment you will have the opportunity to us a spectroscope equipped
with a gas discharge tube and transformer. Each gas discharge tube will contain a pure gas of either
H2, He, Ne, Hg or Ba.
You will need to observe and record the color (of the excited electrons transitioning to a lower
energy state) as well as the emission line spectrum of H2 and one other element (eg. either He, Ne,
Hg or Ba). Important: Inform your instructor which gas discharge tube that you would like to
observe so that your INSTRUCTOR WILL CHANGE THE HOT GAS DISCHARGE TUBES.
(a) Using a spectroscope with H2 gas discharge tube in the transformer, draw the scale and
spectral emission lines using colored pencils. Now repeat this for one other gas discharge
tube containing He, Ne, Hg or Ba.
(b) Please explain in detail, why we see lines and not a continuous spectrum of colors.
(c) In your own works, explain how spectral lines are formed and why the lines have certain
colors.
(d) Estimate the energy, E, frequency, υ and wavelength, λ for each of the spectral lines in the
hydrogen emission spectrum. Show your calculations and compare your results to that
published in the literature.
Materials:
Goggles, nichrome or platinum wire and holder, nine small test tubes, test tube rack, Bunsen burner.
Safety:
The materials you will work with in today’s experiment are concentrated enough to cause serious
skin /eye burns. You must be wearing safety goggles at ALL times and be careful not to spill any of
the solutions on your skin or clothing. If an accident occurs and you spill or get solution on you skin
or in your eyes, immediately rinse with plenty of water and notify your lab instructor. Be careful
lighting and working around the open flame of the Bunsen burner. Do not change the gas discharge
tubes. Your INSTRUCTOR WILL CHANGE THE HOT GAS DISCHARGE TUBES.
Procedure, Part I:
1. You will work with your lab partner in this experiment. Each team will examine emission colors
of 8 known materials. Partners should trade duties so that each person has experience both
generating the flame colors and recording/comparing data.
2. Place approximately 5 mL of 6M Hydrochloric Acid plus samples of the 8 known solutions into 9
small labeled test tubes:
3. Obtain a nichrome or platinum wire with a cork holder or other heat insulating handle.
4. Carefully light the Bunsen burner and adjust the flame for a blue (hottest) center.
5. Dip the metal end of your test wire in the 6M HCl solution and heat the wire in the hottest part of
the flame. Repeat twice. This will clean off your wire so that any metal contaminates present on the
wire will be removed. You will need to repeat this step before examining each different solution.
6. You are now ready to perform the flame tests on the known solutions. Dip the wire into your first
solution and place it in the hottest part of the Bunsen burner flame. Note the color of the flame and
record your observations on your data sheet. You should perform the test a few times to verify
consistency. Make sure you and your partner agree on the color observed.
7. Clean your wire with the 6M HCl as described in step 5. Repeat the tests on the remaining 7
known solutions as described in step 6. Record your observations on the data sheet. Make sure to
clean the wire between solutions to minimize contamination.
8. Select three Unknowns from the 8 available (they are the same materials as knowns, but are
coded U1, U2, U3, etc.) Perform the flame tests on each unknown according to step 6 and record
your observations on the data sheet. Don’t forget to record the identification (eg. coded U1, U2, U3,
etc.) of your unknowns.
9. Make sure that you turn the gas that is connected to your Bunsen burner, off when you are
finished.
Procedure, Part II:
A station containing the spectroscopes and gas discharge tubes will be available for your use. Each
gas discharge tube will contain a pure gas of either H2, He, Ne, Hg or Ba. You will need to observe
and record the color (of the excited electrons transitioning to a lower energy state) as well as the line
emission spectrum of H2 and one other element (eg. either He, Ne, Hg or Ba). Analyze your results
and compare your line emission spectra with those in the literature or internet. Include the literature
or URL citation. Important: Inform your instructor which gas discharge tube that you would like to
observe so that your INSTRUCTOR WILL CHANGE THE HOT GAS DISCHARGE TUBES.
Pre-Lab.
Read the entire experiment, review measurements, scientific notation, the web sites below and
submit the required safety hazards and safe handling practices for all the chemicals that we will use
in this experiment. Please obtain this information from MSDS and include it in your pre-lab
assignment. If you acquire the MSDS from http://sciencelab.com/msdsList.php, you will need to
attach sections: 3, 7, 8, AND 11. See pages 72-73 on Atoms and Light and the electromagnetic
spectrum in your textbook.
CHEM 32A- Flame Test Identification of Elements and Interpreting their
Spectral Lines Using a Spectroscope
Name: ________________________________________________
Date: _____________
Post Lab Questions. You may want to use additional pages.
1.
Name the 3 elements contained in your 3 unknowns via their flame colors.
2.
List 2 safety precautions that you took in today’s experiment.
3.
If you suspected strontium presence in a patient, what color flame would it make?
4.
What is the difference between an “excited” and a “ground” state of an electron?
5.
What is the mathematical relationship between color (wavelength) and energy?
6.
Which has more energy: red, green, or blue light? Why?
7.
Why do we wear sunscreen, what color are we discriminating against and why?
8.
Our eyesight is limited to the “Visible” spectrum, what do we call the two spectral
regions immediately above and below our visible range?
9.
Using a spectroscope connected to a transformer, draw and indicate the color of the spectral
emission lines for H2 and one other element, (either He, Ne, Hg) in a gas discharge tube. Contrast
your results with those found in the literature and discuss your results.
Some flame test references for 32A experiment
General background
http://en.wikipedia.org/wiki/Flame_test;
http://www.amazingrust.com/experiments/how_to/flame_test.html; This reference has more
elements, but no photos http://chemistry.about.com/od/analyticalchemistry/a/flametest.htm;
Color to wavelength charts from NASA
http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/student-worksheet-flame.html;
Wavelengths of various colors
http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html; Article on Color
http://en.wikipedia.org/wiki/Color
Note:
To avoid writing numbers with very large or very small exponential values, we often use descriptive
words to keep numbers small and simple. We typically converse in Kilometers (not thousands of
meters) when driving a car, and microns (not millionths of meters) describing microscopic details.
Terms such as nanometer, picosecond, and gigahertz are commonly used in science and medicine.
Here are the definitions ... including “atto” and “zepto” convenient for noting photon light energy in
this experiment.
DATA SHEET FOR FLAME TEST
SJCC Chemistry, Chem 32A
Student Name _______________________________
Lab Day & Time _____________________
Material used
Known Element
Observed Flame Color
Wavelength, nm
Photon Energy "ZeptoJoules"
0.5M SrCl2
Sr, Strontium
___________________
______________
__________________________
0.5M LiCl
Li, Lithium
___________________
______________
__________________________
0.5M CaCl2
Ca, Calcium
___________________
______________
__________________________
0.5M NaCl
Na, Sodium
___________________
______________
__________________________
0.5M H3BO3
B, Boron
___________________
______________
__________________________
0.5M BaCl2
Ba, Barium
___________________
______________
__________________________
0.5M CuCl2
Cu, Copper
___________________
______________
__________________________
0.5M KCl
K, Potassium
___________________
______________
__________________________
Observed Flame Color
Wavelength, nm
Photon Energy "ZeptoJoules"
Unknown #
Suspected element
__________
________________
___________________
______________
__________________________
__________
________________
___________________
______________
__________________________
__________
________________
___________________
______________
__________________________
Spectra wavelengths using the spectrascope and gas filled discharge tubes
Symbol
Element Name
Observed Color
Wavelength, nm
Photon Energy
H2
Hydrogen
___________________
______________
__________________________
__________
________________
___________________
______________
__________________________
How do your results compare to literature values?
DATA SHEET FOR FLAME TEST
SJCC Chemistry, Chem 32A
If you enter the data in Excel, it can be plotted automatically.
You can also do the plot manually.
An example, to simplify graph label you can use "atto" or "Zepto" joules
650
(convert to meters for calculation)
Wavelength of light λ =
Nanometers
6.50E-07
meters / 10^9 = nanometers
Wavelength of light λ =
Meters
6.6261E-34
universal constant of nature
Planck's Constant h =
Joule*sec
2.9979E+08
universal constant of nature
Speed of light c =
meters/sec
3.0561E-19
want to avoid writing 10^-19 ?
Photon Energy E = hc/λ =
joules
0.306
Joules / 10^18 = AttoJoules
Photon Energy E = hc/λ =
"Atto Joules"
306
Joules / 10^21 = ZeptoJoules
Photon Energy E = hc/λ =
"Zepto Joules"
Using precision graph paper or Excel, construct the graph below using your own data.
4.8
Energy in Joules * 10^-19 --->
4.6
4.4
4.2
4
3.8
3.6
3.4
3.2
3
2.8
400
425
450
475
500
525
550
575
Wavelength in Nanometers --->
600
625
650
675
700